Preliminary studies to evaluate the stability of fentanyl and clonidine in human blood have just been completed. These were necessary to finalize the schedule for research blood draws. After this schedule is finalized, the protocol will be resubmitted to the NCI Institute Review Board for final approval. Patients undergoing isolated hepatic perfusion who are expected to be extubated at the end of the case will, in a prospectively randomized fashion, receive either placebo or Clonidine, 5 mcg/kg intravenously, at the end of the surgical procedure. After awakening and extubation, rescue intravenous morphine will be titrated as needed. Narcotic requirement and patient rating of pain during the first 36 hours, plasma fentanyl and clonidine levels during the first 24 hours and catecholamine levels during the first 12 hours will be followed as well as events of respiratory depression, hypotension and bradycardia requiring pharmacologic intervention.